1. Field of the Invention
The present invention relates to the production of liquid hydrocarbons and more particularly to the production of liquid hydrocarbons using various thermal methods. These thermal methods include using steam to heat the formations to reduce the viscosity of the oil so it can be produced. The use of steam to produce heavy crude deposits has increased in recent years as a result of decreasing worldwide reserves and increasing prices.
2. Description of the Prior Art
In a thermal recovery process using steam, two methods are primarily used. In the first, steam is injected into the formation for a period of time after which the well is shut in and allowed to soak. Following the soaking, the crude oil that accumulates in the well is produced and the process is repeated. In the second method, the steam is used not only to heat the formation but also to drive the crude toward a production well. In both of these methods the steam flows through perforations in the well casing into the formation. It is therefore desirable to know the injection profile of the steam entering the formation through the various perforations in the casing. This information is used to design a particular pattern for introducing the steam into the formation to maximize the production and minimize the steam required. It is necessary to know the formation which the steam is entering and also the quantity of steam entering each formation. This information is necessary to determine the amount of heat being applied to each formation that, in combination with the production resulting from the heat input, can be used to calculate the efficiency of the process.
In U.S. Pat. Nos. 4,581,926 and 4,736,627, there is described a method and apparatus for the downhole measurement of the quantity and quality of the steam being injected into the various formations surrounding a thermal injection well. When used in a well having multiple perforated zones, the invention provides a direct means for determining the amount of thermal energy flowing into each zone. The patents describe methods and apparatus for determining not only the amount of steam that is being injected into each zone but also the quantity of liquid present so that the quality of the steam being injected can also be determined.
In order to determine the quantity of liquid being injected the patents disclose various methods for collecting the liquid which flows primarily down the inner wall of the well casing and then measuring the quantity collected. While the apparatus described has been successful in measuring the quantity of liquid, it is complicated and adds to the overall cost and reliability of the measuring instrument.
In addition to the above, the apparatus also includes a motor/generator set and a turbine wheel that is used to monitor or measure the steam vapor flow. The motor/generator is connected to the surface by multiple conductor cables so that the motor can either be powered to run as a motor or a signal can be taken from the unit when it runs as a generator. As described in the patents, this data can then be used to calculate both the steam flow into each formation at any particular depth in the well, as well as the quality of the steam.
While such an instrument has operated satisfactorily it does require considerable equipment and is expensive to build. The complexity of the instrument increases its operating and maintenance costs.